Technical Field
The invention relates to a thin film transistor substrate and a display panel having the thin film transistor substrate.
Related Art
As the progressive of technology, flat display panels are widely applied to various fields. Because it has advantages of compact volume, low power consumption, and non-radiation, it gradually replaces traditional CRT (cathode ray tube) display device and applies to various electronic products, for example, mobile phone, portable multimedia device, notebook computer, LCD (liquid crystal display) TV or LCD monitor, etc.
Taking liquid crystal display panel for example, a conventional liquid crystal display panel includes a thin film transistor (TFT) substrate, a color filter substrate and a liquid crystal layer. The TFT substrate and the color filter substrate are disposed oppositely, and the liquid crystal layer is sandwiched between the TFT substrate and the color filter substrate. Herein, the TFT substrate has a plurality of thin film transistors and a plurality of pixel electrodes disposed on a substrate, and pixel data are input to these pixel electrodes by controlling the thin film transistors. Accordingly, it controls the liquid crystal molecules of liquid crystal layer to steer and thus displaying the image.
Due to drastic competition in the market, demands of size and display color saturation of the display panel and display device are also rapidly grown. The electrical characteristics and stability of TFT are also urged. Herein, the thin film transistor (hereinafter TFT) based on the metal oxide (Metal oxide-based, MOSs) as the material of the semiconductor layer can be manufactured at room temperature, and it is beneficial to good current output characteristics, low leakage current and electron mobility higher than ten times of that of the amorphous silicon TFT (a-Si TFT). It respectively reduces the power consumption of the display panel and to enhance the display panel of the operating frequency. Therefore, it becomes the major driving element utilized in next generation display panel and apparatus.
However, the metal oxide semiconductor (MOS) layer has better electrical properties, but during manufacturing TFT, when the source or drain of TFT employs metal layer containing aluminum in form of single layer or multiple layers (e.g., multiple metal layers of molybdenum nitride/aluminum/molybdenum nitride) and they are patterned by wet etching, the reaction product by etching causes damages on the channel layer of the oxide semiconductor after subsequent heat processes. Referring to FIG. 1, the initial voltage of TFT is offset from the normal curve C1 to negative bias curve C2. Therefore, it influences the operation reliability of TFT device and further influences the reliability of the display panel.
Therefore, it is an important subject to provide a TFT substrate and its display panel which have better device reliability and improved product yield.